This invention is concerned with the electrodeposition of copper from aqueous acidic baths. More particularly this invention is concerned with an aqueous acidic bath for the electrodeposition of copper containing additives which provide bright and leveled copper electrodeposits and to a process for electrodepositing copper employing said bath.
In the past a large number of agents have been described in the art for use in electroplating baths alone or in combination to improve the quality of the electrodeposit in terms of brightness, surface smoothness, hardening, leveling and to increase th lower limiting current density of deposition.
The present invention has as its object the formation of bright and leveled copper electrodeposits from an aqueous acidic bath, particularly an aqueous acidic sulfate bath by adding to such bath certain additives. The term "leveled" denotes a copper deposit whose surface is smoother than its substrate. The term "bright" indicates that the formed electrodeposit is characterized by having a uniform highly reflective surface gloss over most of its surface. Generally leveling and brightness vary with the current density at the cathode, all other factors such as copper salt concentration, pH, type of acid, temperature etc. being equal. As the current density decreases brightness of the electrodeposit tends to decrease often diminishing to a haze which may be unacceptable for many commercial applications. The strength of leveling also varies with current density.
The present invention provides bright copper electrodeposits over a wide current density range including low current densities on the order of 0.4 amps. sq. dm. or less with strong leveling properties throughout. The high degree and rate of leveling achieved according to the present invention translates to economy in the finishing costs of the electrodeposited substrate and in the materials necessary therefor. The improved low current density brightness, that is the widening of the bright current density range, according to the invention allows strongly profiled objects to be electroplated with substantially uniform brightness. The additives also prevent roughness formation at high current densities and increase hardness of the electrodeposit.